For a long time the idea that a “runner’s high” occurs after exercise of a long duration has been obvious to athletes. The physiological reasons behind it, however, have been much more of a mystery to scientists. The most prominent theory to explain it over the last twenty years or so has been the endorphin hypothesis, which suggests that prolonged strenuous activity releases endorphins, causing an elevation of mood and decrease in the perception of pain. The word endorphin comes from “endogenous”, meaning produced within the body, and “morphine”, an opiate known for its pain-mitigating properties. Thus, endorphins are like opiates created by our bodies, and can act as natural painkillers or induce euphoric feelings under certain circumstances.

In the PET, they used a radioactive opioidergic ligand 6-O-(2-[F] fluoroethyl)-6-O-desmethyldiprenorphine ([18F]FDPN). This substance binds to opiate receptors in the brain. If opiate receptors are in use by endorphins, the [18F]FDPN should be unable to bind to those receptors. Thus, if intense exercise produces endorphins, they will occupy opiate receptors, and, as compared to the PET scan at rest, there should be more [18F]FDPN in an unbound state, as its natural binding site will be filled by endorphins.

This is just what the researchers found. After the exercise, opioid receptors showed decreased availability (meaning they were bound to endorphins produced by the running). The level of euphoria as reported by the athletes was significantly increased, with higher levels inversely correlated with the availability of opiate receptors. The brain regions most affected were primarily in prefrontal and limbic areas, areas commonly associated with emotions.

The researchers hope to expand upon this study by searching for practical uses for the improved understanding of acitivity-induced endorphin binding. This could include investigating the specific benefits of exercise for those suffering from chronic pain, depression, or anxiety. They also are very interested in how genetic makeup affects opiate receptor distribution in the brain, and how this might affect addiction.

Another concept (albeit a less substantiated one than the occurrence of runner’s high) under investigation of late is the benefit of aromatherapy. Aromatherapy is an alternative medical practice that has been around for centuries, but has regained a great deal of popularity over the last couple of decades. It involves the inhalation of certain scents, such as lavender or lemon, which are purported to have a number of positive effects on one’s mood and health.

Researchers from Ohio State University put aromatherapy to the test in what is probably the most comprehensive study on the practice to date. Using 56 participants, some who advocated the use of aromatherapy and others who had no opinion, the researchers measured blood pressure, heart rate, healing ability, stress hormone levels, reaction to pain, and recorded self-report of mood over a three-day period of aromatherapy use. The participants were exposed to an odor suggested to be a stimulant (lemon), another purported to be relaxing (lavender), and water with no odor. Some of the participants were told what odors they would be subjected to, and what changes they might expect, while others were randomly placed in a blind category where no such information was given. The experimenters were all kept in a blind condition.

The lemon oil did induce an enhancement of mood based on self-report, although the lavender oil did not. Neither of the oils, however, had any effect on the numerous biochemical markers used to measure stress, healing ability, immune response, or pain tolerance.

The researchers who conducted the study are quick to point out this is not conclusive evidence there is no benefit to aromatherapy. As one of the authors stated, however, “…we still failed to find any quantitative indication that these oils provide any physiological effect for people in general”. It's something to keep in mind if you are thinking of buying any alternative medicine products that tout their immune-boosting, stress-relieving, and mood-enhancing qualities: are their claims backed by science, or just anecdotal evidence?

Neuroscientifically Challenged

Neuroscientifically Challenged is a neuroscience learning resource. In addition to a blog that discusses science current events in a non-technical manner, you will also find a number of videos and articles that you can use to learn about basic principles of science and the brain.